The present invention relates to a data transfer switch and, more particularly, to a data transfer switch for transferring and outputting data of an arbitrary length input from a predetermined input accommodation unit to a predetermined output accommodation unit.
A conventional data transfer switch having a plurality of input accommodation units (input ports) and output accommodation units (output ports) to transfer data of an arbitrary length from an arbitrary input accommodation unit to an output accommodation unit through a predetermined medium (physical medium) has an arrangement shown in FIG. 13.
In input accommodation units 101a to 101n, transfer requests 105a to 105n are output from input controllers 113 to a system bus controller 103 to request data transfer through a medium, i.e., a system bus 104 in response to external data write access to memories 111.
In response to these transfer requests, the system bus controller 103 checks the use state of the system bus 104 and outputs transfer permissions 106a to 106n to the input controllers 113 to permit data transfer if the system bus 104 is free.
Upon reception of the transfer permissions 106a to 106n, the input controllers 113 designate the start of data transfer to data transfer sections 112. The data transfer sections 112 read out data from the corresponding memories 111 and output the readout data onto the system bus 104.
In output accommodation units 102a to 102n, data receiving sections 121 receive data of the corresponding ports from the system bus 104 and write them in corresponding memories 122, thereby completing the data transfer. The data are externally read out from the memories 122 at subsequent predetermined timings.
In this conventional data transfer switch, the plurality of input accommodation units and the plurality of output accommodation units share the medium (physical medium), i.e., the system bus 104. To use this medium, the transfer requests are arbitrated or scheduled in accordance with predetermined rules, thereby performing data transfer between an arbitrary input accommodation unit and an arbitrary output accommodation unit. For this reason, the sum of output transfer rates capable of outputting data from the respective input accommodation units and the sum of input transfer rates capable of receiving data by the respective output accommodation units are limited by the data transfer rate of this physical medium (electrical transfer rate of the physical medium). When the data output transfer rate of each input accommodation unit and the data input transfer rate of each output accommodation unit come close to the data transfer rate of the medium, the numbers of input and output accommodation units are undesirably limited.
Another conventional switch is also proposed to increase the data transfer rate of the medium itself. In this switch, a tag representing an output destination is imparted to data in an input accommodation unit, and data are distributed at an intersection constituting a transfer switch on the basis of the tag. With this arrangement, when a plurality of data for the same destination simultaneously reach the intersection, a data loss occurs. To avoid this, a queue buffer must be arranged to perform contention control. The buffer capacity is undesirably increased with an increase in the number of intersections.